SOCT: Secure Outsourcing Computation Toolkit Using Threshold ElGamal Algorithm

Abstract

Cloud computing offers inexpensive and scalable solutions for data processing, however privacy concerns often hinder the outsourcing of sensitive information. Homomorphic encryption provides a promising approach for secure computations over encrypted data. However, existing models often rely on restrictive assumptions, such as semi-honest adversaries and inaccessible public data. To address these limitations, we introduce the Secure Outsourcing Computation Toolkit (SOCT), which is a novel framework based on the threshold ElGamal cryptosystem. The toolkit employs a dual-server decryption architecture using a (2,2) threshold additively homomorphic ElGamal (TAHEG) algorithm. This architecture ensures that ciphertexts can be decrypted only with the cooperation of both servers, mitigating the risk of data breaches. The TAHEG algorithm requires the input of a secret key for every decryption operation, preventing unauthorized access to plaintext data. Moreover, the key generation process does not burden users with generating or distributing partial secret keys. We provide rigorous security proofs for our threshold ElGamal cryptosystem and associated secure computation functions. Experimental results demonstrate that SOCT achieves significant efficiency gains compared to existing toolkits, making it a practical choice for privacy-preserving data outsourcing.